/Engine/Source/Runtime/Engine/Classes/Engine/GameInstance.h
Retrieves the name of the online subsystem for the platform used by this instance. This will be used as the value of the PlayerOnlinePlatformName parameter in the NMT_Login message when this client connects to a server. Normally this will be the same as the DefaultPlatformService config value, but games may override it if they need non-default behavior (for example, if they are using multiple online subsystems at the same time).
virtual [FName](API\Runtime\Core\UObject\FName) GetOnlinePlatformName() const